Put the flour, butter, egg and egg yolk in a food processor and blend until a soft dough is formed. If the pastry won't come together, add a drop of cold water. Take the dough out of the processor and knead lightly for 1 minute until it is smooth. Place it in a freezer bag or wrap in clingfilm and chill in the refrigerator for at least 30 minutes. Alternatively, make the pastry by hand by rubbing the butter into the flour until it resembles breadcrumbs, then working in the eggs.
Roll the pastry out on a well-floured work surface until it is about 3 mm (⅛ inch) thick and line a 25 cm (10 inch) round, fluted tart tin. Trim off the excess pastry. Chill the lined tart tin for 1 hour.
Line the tart with a piece of nonstick baking paper, cover with baking beans, then place in a preheated oven, 180°C (350°F), Gas Mark 4, for 10–12 minutes until lightly golden. Remove from the oven and take away the baking paper and beans. Place back in the oven for a further 2 minutes to dry out the base of the pastry case. Remove from the oven.
Slice each asparagus spear into 3 on the angle. Flake the fish into the pastry case and add the asparagus. Mix together the eggs, milk and cream. Season with salt and pepper. Pour the mixture into the pastry case and cook it in the oven for 20–25 minutes until the mixture has set.